Buildings having steel frameworks are particularly vulnerable to collapse in the event of a fire. Steel loses its strength as the temperature rises. By insulating the steel, the rate of heat transfer can be reduced, which can extend the time the building remains intact, giving more time for evacuation.
Passive fire protection is the term generally given to systems which rely on insulation to protect buildings from fire. Passive fire protection may be “reactive” or “non-reactive”. Reactive systems are based on insulation which changes its physical and/or chemical nature in response to fire. Examples include intumescent, oblative and subliming systems. Non-reactive systems provide insulation without the need for any chemical or physical change. Examples include cementitious spray and vermiculite board.
Fire-protective coatings may be applied to steel framework for buildings either off-site (in the steel yard) or on-site (to the erected framework). Typical intumescent systems are based on a mixture of ammonium polyphosphate and melamine. These react to produce N2 gas which results in a layer of foam several centimetres thick which insulates the framework.
Conventional one-component intumescent compositions are either solvent or water-based and form a dry film through evaporation of the solvent or water. This characteristic places practical limits on the maximum wet film thickness that can be applied in any one coat, as thick films tend to take a long time to dry.
Two-part epoxy resin based coatings have been used by Leigh's Paints to provide fire protective coatings on steel. Such coatings have excellent adhesion to steel, are hardwearing and rely on intumescence to provide fire protection.
Similarly, CharTek have developed a variety of products for use as fire protective coatings. CharTek 7, for instance, is a solvent-free, reinforced epoxy intumescent fire proofing coating, suitable to protect steelwork in a hydrocarbon fire.
Fire protective intumescent coatings are described extensively in the patent literature. US 2008/0224105 A1, for instance, describes a liquid intumescent coating composition comprising a resin system. The coating composition is curable to a solid state in a free radical polymerisation reaction. WO 2008/129242 describes an intumescent formulation comprising a source of carbon, a blowing agent, an acid source and clay such as an organoclay. The organoclay is thought to improve the thermal barrier properties of a foamed intumescent coating. WO2009/013532 describes a coating composition which comprises at least one intumescent ingredient incorporated into a resin binder which contains at least one covalently bonded phosphorous containing component.
However, these prior art compositions have limited intumescence-generating ability and as a result, thick layers of the compositions are required, which can be very expensive.